In the field of electro-acoustic products, the microphone is a sensor that converts acoustic energy into electrical energy. A capacitive micro-electro-mechanical system (MEMS) microphone generally includes a vibration membrane, a fixed plate (back plate), and a cavity between the vibration membrane and the fixed plate. A capacitive MEMS microphone enables detection of a capacitive value change due to the displacement of the vibration membrane caused by a change in the acoustic pressure, and the detected capacitive value change is then converted to an electrical signal for processing.
The vibration membrane and the fixed plate may come into contact when the vibration membrane is in vibration. Once the vibration membrane and the fixed plate come into contact with each other, they may adhere to each other, and the microphone may not operate correctly. Therefore, a special structure (e.g., a stopper) needs to be designed to prevent the vibration membrane and the fixed plate from coming into contact with each other.
The adhesion probability between the vibration membrane and the fixed plate has a positive correlation with the surface area size of the stopper, that is, the smaller the surface area of the stopper, the smaller the adhesion probability between the vibration membrane and the fixed plate. Thus, attempts have been made to minimize the surface area of the stopper.
FIG. 1 is a cross-sectional view illustrating a morphology of a stopper according to a conventional manufacturing process. As shown in FIG. 1, a first sacrificial layer 101 is formed having an opening 111, then a second sacrificial layer 102 is formed on first sacrificial layer 101. Second sacrificial layer 102 has an opening 112 at a location corresponding to opening 111. Opening 112 defines the shape of a later formed stopper.
In order to reduce the surface area of the stopper, opening 111 has generally a relatively small size that causes opening 112 to have a narrow middle portion and wide end portions. When second sacrificial layer 102 has a relatively large thickness, voids may be present in opening 111, which may affect the shape of a later-formed stopper. A stopper having the shape shown in FIG. 1 may break when the microphone vibrates, thereby losing its effectiveness to prevent an adhesion between the vibration membrane and the fixed plate.